The purification and characterization of the DNA polymerases from normal human brain and brains from patients with Guamanian & U.S. amyotrophic laterial sclerosis will be performed. Characterizations of partially purified polymerases include determining optimum reaction conditions, size, template preference, and primarily the ability to copy natural RNA. These studies are aimed at delineating a viral reverse transcriptase in diseased brains. The antigenic relatedness of relevant ALS/PD DNA polymerases with known reverse transcriptase from murine and primate RNA-tumor viruses will be determined.